Communication between a fixed network and a movable network with means for suspending operation of the moveable network

ABSTRACT

A satellite telephone system for communication between a fixed network ( 4 ) and a moveable network ( 1 ) on board a vehicle, has means for suspending operation of the moveable network, for example when the moveable network could interfere with a fixed network, during safety-critical stages of a flight, or to enforce “quiet” periods on board. When operation of the moveable network ( 1 ) is suspended a control signal is transmitted to the fixed network ( 4 ), causing the fixed network ( 4 ) to intercept calls directed to the moveable network, thereby avoiding unnecessary signal traffic over the satellite link ( 3, 6, 13 ). The moveable network may be a wireless network ( FIGS. 1 , 2), or a wired network ( FIG. 4 ).

This invention relates to mobile telephony, and in particular to systemsfor use on board vehicles.

There has been considerable activity in recent years in proposals toallow the use of mobile telephones in environments where conventionalcellular telephony base stations cannot provide coverage, in particularon board ships and aircraft. These vehicles frequently travel beyond therange of land-based cellular base stations, which typically have a rangeof the order of 1 to 10 km.

There are a number of special difficulties to be addressed if a standardcellular telephone is to be used in an aircraft. Firstly, many cellularbase stations have antennas arranged for maximum gain in the horizontalplane, so an airborne cellular telephone may not be able to obtain asignal from any base station, even when flying over land served by acellular base station network. If the range of the base stations doesextend to the normal flying height of aircraft, frequency re-usepatterns, which allow several base stations to use the same radiofrequencies without interference, are designed on the assumption that amobile unit served by one base station is not able to exchange radiosignals with other base stations using the same frequency. Thisassumption ceases to be valid if a mobile unit is several thousandmeters above the ground, since it may be in line-of-sight of a largenumber of base stations simultaneously. Moreover, although reliablehandover of a mobile unit can be achieved from moving vehiclestravelling at speeds of up to 200 km/h, a typical passenger aircrafttravels at speeds approaching 1000 km/h. Airlines also imposerestrictions on the use of powerful radio signals on board, as aprecaution against possible interference with the aircraft's electronicsystems.

For truly global coverage, satellite telephones are available. However,these are expensive and much heavier than a cellular telephone. Bothcellular telephones and satellite telephones also suffer from thescreening effect of being inside a metal hulled vehicle. As withcellular telephones, the unrestricted use of a portable satellitetelephone within an aircraft may be prohibited.

A user without his own satellite telephone may use special facilitiesprovided on board, such as the service provided to several airlines bythe applicant company under the Registered Trade Mark “Skyphone”. Thisuses onboard terminals connected, through a satellite link between theaircraft and a satellite ground station, to the telephone network.Another system, TFTS (terrestrial flight telephony system, marketed as“Jetphone”), operates in a similar manner, but uses a direct linkbetween the aircraft and the ground station, without a satellite link.Similar systems are provided on board ships. However payment for theseservices is generally at the point of use (or prepaid), and may be in aforeign currency. Calls made to the user's cellular telephone will notbe successful unless the calls can be diverted to the telephone numberof the onboard user terminal (which will generally not be known to thecaller), and any special facilities offered by the user's cellularnetwork will in general be unavailable. A user with his own cellulartelephone account which, through “roaming” agreements between networkoperators, can be used in many different countries, would thereforeprefer to continue to use his cellular telephone subscription whentravelling within or between these countries on board an aircraft orother vehicle.

Proposals have been made, for example EP0915577 (Rohde & Schwartz) for afacility which would allow cellular telephones to make outgoing calls byway of the aircraft's own onboard telephone system. This allows theaircraft's onboard systems to impose power control on the mobile unitsand ensure that their radio transmissions are kept within safe limits.However, the cellular telephone is not directly connected to thecellular network, so conventional cellular radio location updateprocesses cannot be used to inform the user's home network of itscurrent location and allow incoming calls to be routed to the telephone.

Proposals have also been made to allow a user to use his own cellularradio identity when using the satellite facility, instead of a specialidentity under the satellite system. This would allow billing to be madethrough the user's normal cellular radio account, and would also allowincoming calls made to his cellular telephone number to be receivedwhilst travelling. To this end, systems have been developed which allowcall diversions to be set up to allow calls made to the user's cellularnumber to be transferred to a destination node of the tracking radiosystem. The destination node may be an onboard handset temporarilyallocated the user's cellular identity, or it may be an onboard basestation capable of wireless connection to the user's own cellulartelephone. Systems of this general kind have been disclosed inInternational Patent Applications WO99/12227 (Nokia), WO94/28684(Nordictel) and WO98/26521 (Ericsson); European Patent Applications0920147 (Alcatel) and 0915577 (Rohde & Schwartz), and United KingdomPatent Application 2310973 (Motorola). An onboard base station can beintegrated with other onboard systems, allowing local control of thebase station's transmitter, and those of the mobile units with which itis co-operating, so as to keep their power within permitted limits.

There are a number of circumstances in which an onboard system needs tobe switched off. For example, when an aircraft is close to or on theground, or a ship is close to shore, the onboard cellular base stationcould interfere with ordinary cellular base stations nearby. TheINMARSAT geostationary satellite system covers the entire planet withonly several satellites, but nevertheless on long distance flights,particularly transpolar flights, an aircraft may be unable to retaincontact with the same satellite throughout. It may therefore benecessary for an aircraft's satellite system to change the satellitethrough which it is communicating, which necessitates a change in theaddressing of all its telephone nodes, and hence to the call diversioninstructions relating to any cellular user on board. It may be necessaryto shut the onboard system down for a short period whilst this is done.

It may also be desirable to shut the system down during safety-criticalstages of a flight, or to enforce designated “quiet” periods on board.Furthermore, when the vehicle completes its journey, it is desirable toshut down the system to allow the users to register their cellularhandsets with the local cellular network in the normal way once theyhave alighted.

However, whilst the system is shut down, any incoming calls willcontinue to be directed to the onboard system, causing unnecessarysignalling traffic over the satellite link. The present inventionrelates to a method for avoiding this problem.

According to the invention there is provided a method of controlling atelephone system for communication between a fixed network and amoveable network, the system having means for suspending operation ofthe moveable network, wherein when operation of the moveable network issuspended a control signal is transmitted to the fixed network, causingthe fixed network to intercept calls directed to the moveable network. Afurther control signal is transmitted when operation of the moveablenetwork is resumed, causing the fixed network to cease to interceptcalls.

Embodiments of the invention will now be described with reference to theFigures, in which:

FIG. 1 is a schematic diagram showing the functional relationshipsbetween the systems which co-operate to form one embodiment of theinvention

FIG. 2 is a more detailed schematic diagram of the network terminationand associated card reading equipment, which for illustrative purposeswill be assumed to be on board an aircraft

FIG. 3 is a diagram showing part of an alternative arrangement ofnetwork termination, arranged for co-operation with a cellular telephonehandset

FIG. 4 is a schematic diagram showing the functional relationshipsbetween the components of the fixed part of the first telecommunicationssystem which co-operate in the invention,

FIG. 5 is a schematic diagram of the switching system, interface unit,and associated parts of the second telecommunications system;

FIG. 6 is a flow chart showing the process by which a diversion is setup in the second network to a termination connected to the first network

FIG. 7 is a flow chart showing the process by which a call coming in tothe second network is connected to a telephone connected to the firstnetwork

FIG. 8 is a flow chart showing the process by which the second networkrestores the original settings for a telephone when it disconnects fromthe first network.

FIG. 9 illustrates the forwarding process implemented to a data message.

FIG. 10 illustrates a conditional forwarding process for a data message.

FIGS. 11 and 12 show the general arrangement of the various componentswhich co-operate in a second embodiment of the invention: FIG. 11 showsthe moveable vehicle-borne parts and FIG. 12 the fixed, ground based,parts.

FIGS. 13 and 14 show the method of operation of this embodiment

FIGS. 15, 16 and 17 illustrate three further embodiments of theinvention.

FIG. 18 illustrates a power control process for use with the embodimentsof FIGS. 15, 16 and 17.

FIG. 19 is a flow chart showing a call diversion process according tothe present invention, for use when the system has to be temporarilyshut down.

All these embodiments illustrate the invention using a standard switchedcellular network, using the terminology of the “GSM” standard forillustrative purposes. However, the invention is applicable to othercellular networks, including packet networks, which are used to carrydata over a distributed computer network such as the “Internet”,carrying messages using formats such as the “Internet Protocol” (IP).Thus, unless the context clearly demands otherwise, any reference inthis specification to switching includes the equivalent routingfunctions in a packet network of this kind.

The first embodiment is illustrated in FIGS. 1 to 10. FIG. 1 shows thegeneral arrangement of the various components which co-operate in thisembodiment. Note that traffic links (which can carry speech, data, etc)are shown as full lines, signalling links used only for call set up areshown as broken lines.

The onboard part 2 (shown in more detail in FIG. 2) comprises one ormore handsets 25 (which, in the alternative arrangement of FIG. 3, arethe users' own cellular telephone handsets 31), connected to atermination point 20 of the satellite network. The termination point 20is in communication with a ground station 4, shown in more detail inFIG. 4. In this embodiment, the communication link is made through anearth-orbiting satellite 6.

The principal components of the ground station 4 relevant to thisinvention are an antenna 44 which communicates, by way of the satellite6, with the onboard system 2, an Access Control and Signalling Equipment(ACSE) 40 which carries out call switching functions to allow calls tobe placed through the public switched telephone network (PSTN) 8 toother telephones 85, and a Card Management System 42 which authorisesthe use of an individual terminals 25 according to user identitiesentered with respect to that terminal. There is also a register 43 ofcard identities, to provide a correspondence between the user identitiesused by the satellite terminal and the corresponding cellular telephoneuser identities (not necessary if the cellular telephone identity isread directly by the terminal 20, as will be described with reference toFIG. 3), and to provide billing information.

The card management system 42 interacts with an interface unit 52 of a“host” cellular telephone network 5, shown in more detail in FIG. 5.This network 5 is connected to the public switched telephone network(PSTN) 8 and to other cellular networks 7 through a switching centre 50.Associated with the interface unit 52 there is an “aircraft locationregister” 41 which monitors the terminals currently served by eachindividual satellite, and modifies the functioning of the interface unit52 when a terminal 20, for example on board an aircraft 2, moves fromthe coverage area of one satellite 6 (and its ground station 4) toanother.

The cellular network 7 illustrates in simplified form the systemarchitecture of a “GSM”-standard cellular radio system, and theterminology used in this standard. The network 7 has a switching system(MSC) 70 to allow connection of one or more base transceiver sites (BTS)74, through one or more base site control systems 72, to the PSTN 8 andthus to other telephones 85. A mobile telephone 75 may establish radiocontact with one of the base stations 74 in order to make and receivetelephone calls. The network 7 also includes a “Visitor LocationRegister” 7.1, which maintains details of those cellular telephones 75currently co-operating with the network 7. Mobile telephones accordingto the “GSM” standard are capable of co-operating with differentnetworks (“roaming” between networks). To allow this to take place, whena mobile telephone 75 changes from one network to another, the networkto which it has moved retrieves data from a “Home Location Register” 73permanently associated with the handset 75. The network 7 in which theHome Location Register 73 associated with a given handset is to be foundis identifiable from the handset's identity code. The Home LocationRegister also records the identity of the network 7 with which themobile handset 75 is currently operating.

The “host” network 5 operates like conventional cellular network, but isprovided with an interface unit 52, which interacts with the mobileswitching centre 50 as a base site controller would. This interface unit52 may be in addition to one or more base site controllers (not shown).The interface unit does not interact with any base transceiver sites ormobile handsets, but obtains user details (in particular the identity ofa mobile handset) from the card management system 42 to allow it toappear to the switching centre 50, and the HLR 73 in the user's homenetwork, that it is in radio communication with a mobile handset 25. Itcan then control the call forwarding instructions stored in the hostnetwork's VLR 51, to cause incoming calls directed to that handset to bediverted, through the switching system 40 of the satellite network 4, tothe satellite terminal 20.

FIGS. 2, 3 and 4 illustrate this embodiment of the invention in moredetail, applied to a satellite telephone system such as that provided bythe applicant company under the Registered Trade Mark “Skyphone”. FIG. 2shows a first embodiment of the mobile part which has a standard cardreader, whilst FIG. 3 shows an alternative arrangement which allows auser to use his cellular telephone handset. FIG. 4 shows the groundstation.

The onboard system 20 shown in FIG. 2 comprises a plurality of userterminals 21, 21 a (only one shown in detail), connected by a multiplexand radio interface unit 28 to an antenna 29 which provides radiocommunication with a satellite 6. Each user terminal 21 has a cardreading unit 23 into which an intending user can insert a card 24 orother data carrier providing user identification data. The data may givedetails of the user's credit card account, or a special account for theuse of the onboard telephone service. The card reader 23 may be adaptedto read the SIM (Subscriber Identity Module) of a GSM-standard cellulartelephone. (It should be noted that one variant of the method accordingto the invention does not make use of the card reading apparatus23,24,26, although it may nevertheless be present for use by othercustomers of the satellite system).

Further user terminals 21 a may be set aside for non-voice applications,for example an onboard facsimile machine.

The user handset 25 provides the usual keypad, microphone and earphoneto allow the user to make telephone calls. The user handset 25 and thecard reader 23 are both connected to a processor 26 which converts dataread from the card 24, and keystrokes input from the handset 25, intodata signals for transmission over the radio link 29. It also providesidentification data indicative of which of the terminals 21 it is. Afurther processor 27 performs analogue/digital conversion of speechsignals from the handset 25.

The digitised signals from each terminal 21 are multiplexed andmodulated onto a radio carrier in a interface unit 28, and transmittedfrom the antenna 29.

The antenna 29 also receives signals which are demodulated anddemultiplexed in the unit 28. Data signals are processed in theprocessor 26, whilst digitised speech is converted to analogue speech inthe analogue/digital converter 27 and fed to the handset 25.

The interface unit 28 also includes a connection to the data bus 22 ofthe aircraft 2 giving access to aircraft parameters such asundercarriage deployment, “weight-on-wheels”, time to destination,altitude, etc. When a predetermined condition indicative of theimpending end of a flight is met, the interface unit 28 transmits asignal to the ground station to cause a deregistration signal to betransmitted to the card management system 42.

Because the onboard telephone system was originally designed for makingoutgoing calls only, the handsets 25 provided in existing terminals 21are not equipped with a suitable incoming call alerting device. Thehandsets 25 could be modified to provide a buzzer or light to alert theuser to an incoming call. Alternatively, to avoid distracting otherpassengers on the aircraft, the telephone terminal 21 may be connectedto an at-seat entertainment system 200, to provide an alert eitherthrough the earpieces 202 or on the screen 201.

Instead of the terminals 25, an alternative arrangement may be used asshown in FIG. 3. In this arrangement each onboard terminal 25 isreplaced by an onboard interface device 311 to which a user's own mobileradio telephone 31 can be connected electrically, thereby allowing themobile telephone to be used without using its radio antenna. It is amodification of the system described in the applicant company'sInternational Patent Application WO97/36442, published on 2 Oct. 1997,to which the reader is referred for further details. In this modifiedversion a GSM (Global System for Mobile communication) mobile telephone31 comprises r.f. transceiver circuitry 32 coupled to an antenna 33,base band signal processing and control circuitry 34, a rechargeablebattery pack 35, a switch 36 and a socket 37. The processing and controlcircuitry 34 has a data output terminal 34 a coupled to both the r.f.transceiver circuitry 32 and a first contact 37 a of the socket 37. Adata input terminal 34 b of the processing and control circuitry 34 iscoupled to the r.f. circuitry 32 and a second contact 37 b of the socket37. A third contact 37 c of the socket 37 is coupled to a control inputof the processing and control circuitry 34. Fourth and fifth contacts 37d, 37 e of the socket 37, which are respectively for 0V and +V powersupply lines, power the telephone 31, and may also be arranged torecharge its batteries 35. The +V terminal of the battery pack 35 isalso connected to the processing and control circuitry 34 and to aninput terminal of the switch 36. The output terminal of the switch 36 iscoupled to a +V input terminal of the r.f. circuitry 32. A controlterminal of the switch 36 is coupled to an output of the processing andcontrol circuitry 34.

The interface unit 311 comprises a control circuit 312, a user inputunit 313, including a keypad and a display, a V.24 33.6 kbit/s modem314, a power supply unit 315 and a plug 316. The plug 316 has fivecontacts 316 a-316 e which correspond to contacts 37 a-7 e of the socket37 of the mobile telephone 31. The first contact 316 a of the plug 316is coupled to a data input terminal of the control circuit 312 and thesecond contact 316 b of the plug 316 is coupled to a data outputterminal of the control circuit 312. A bi-directional serial link 318 isprovided between the control circuit 312 and the modem 314 for modemcontrol and data signals. The third contact 316 c and fifth contact 316e of the plug 316 are coupled to the +V output of the power supply unit315. The fourth contact 316 d of the plug 316 is coupled to theinterface unit's 0V supply wiring. The user input unit 313 is coupled tothe control circuit 312 for the input of user commands and the output ofdisplay control signals from the control unit 312 to the user input unit313. The +V output of the power supply unit 315 is also coupled to +Vinput terminals 312 a, 313 a, 314 a of the control circuit 312, the userinput unit 313 and the modem 314. The modem 314 is coupled to atelephone line 317 and the power supply unit 315 is arranged to receivepower from an electricity supply 319.

When the user wishes to connect to the interface unit 311, he connectsthe plug 316 of the interface unit 311 to the socket 37 on his telephone31 by a cable (not shown). The voltage on the third contact 37 c of thesocket 37 is detected by the processing and control circuitry 34 whichthereby determines that the telephone 31 has been connected to theinterface unit 311. The connection of the battery 35 to the power supply315 by way of the connections 37 d/316 d and 37 e/316 e also allows thebattery to be recharged.

Once the processing and control circuitry 34 has determined that thetelephone 31 has been connected to the interface unit 311, it sends acontrol signal to the switch 36, causing it to open, isolating the r.f.circuitry 32 from the battery pack 35 and the power supply 315 in theinterface unit 311. The processing and control circuitry 34 alsoresponds to the voltage on the third contact 37 c of the socket 37 byselecting alternative control programs or constant data to allow fordelays in the signal path from the telephone 31 to the controller 30which are caused by the use of the satellite link 6 and the modems 314,32.

In this arrangement, instead of the need for a separate card reader 23,the telephone 31 identifies itself to the telephone network 40/42 bygenerating its terminal identity code (IMSI in the case of a GSMtelephone). The registration signal is not transmitted from the antenna3 because the r.f. circuitry 32 is disabled. Instead, it is output tothe interface unit 311 via the first contacts 37 a, 316 a of the socket37 and plug 316.

The operation of the onboard system will now be described with referenceto FIG. 6. When the card reader 23 or interface unit 311 detects thepresence of a card 24 or handset 31 respectively, (step 601) itgenerates a prompt to indicate to the user that he may wish to havecalls diverted to the onboard system. If the user requires this service,he enters a code on the keypad of the handset 25, 31 which causes adivert request to be generated (step 602). The details from the card 23(or SIM of the handset 31) are then passed to the processor 26 whichalso provides the identity of the terminal 21 (step 603) and transmitsthe data to the interface unit 28.

Alternatively, these steps (602, 603) may be activated by the userwithout a card, by dialing an access code (divert request 602) followedby further keystrokes to identify the account to be used (terminalidentity step 603). These keystrokes may include the user's MSISDN(which, as his own directory number would be known to him). To preventmisuse of the system by unauthorised personnel, a security code(Personal Identification Number: “PIN”) may be added. This code may havebeen issued previously to the user, or the user may request such a codeby making a call using the satellite system to his home network'scustomer service department and providing personal details to theoperator to prove his identity.

The user may select for the identity of a terminal 21 a other than hisown at seat terminal 21 to be selected as the destination for incomingcalls. For example, if his MSISDN code (or one of them) relates to afacsimile machine having cellular capability, he may request thatincoming calls to that number be directed to an onboard facsimilemachine 21 a.

The data received by the interface unit 28 is then transmitted to theground station 4 (step 604). The further steps (605-615) in the processare carried out by the co-operating networks 4, 5 and will be describedlater.

If the user decides that he no longer wishes to have his calls divertedto the terminal 21, he may cancel the diversion instruction by enteringa special code on the keypad of the handset 25, 31. Disconnect codes mayalso be generated in the interface unit 28 for all the terminationpoints 21, either by the cabin crew or automatically in response to asignal detected on the aircraft's data bus 22 which is indicative of theimminent end of the journey, such as undercarriage deployment, weight onwheels, low altitude, or time remaining to destination as determined bythe aircraft's flight management system. The disconnect instruction istransmitted (step 801, FIG. 8) by way of the switching system 40 in theground station 4, to the interface unit 52 whose operation (steps 802 to805) will be described later.

The Ground Station 4 shown in FIG. 4 has a radio antenna system 44 forcommunicating with the terminal 20, through a satellite link 6 orotherwise. Signals are handled by an Access Control Signalling Equipment(ACSE) 40 which carries out switching functions to route calls to orfrom the public switched telephone network (PSTN) 8.

A card management system 42 comprises a data acquisition unit 47 whichreads data transmitted from the card reader 24, and/or keyed in by theuser, to identify the type of user, confirm the user's account detailsand arrange billing for any calls made, through a billing system 45which raises invoices, or interacts with the systems of a credit cardoperator or bank.

In existing onboard systems a user cannot receive calls, unless thecaller knows the unique “AES” number of the handset 21, 21 a. This isunlikely, as the number depends on the identity of the aircraft, theseat, and the serving satellite or base station.

The equipment just described is augmented in the present embodiment byan interface 46 with the host network 5, and through that to the HomeLocation Register 73 of each network 7 (FIG. 1) whose subscribers are tobe given access to the service, which stores a concordance between thecard identities and the cardholder's cellular radio telephone number(MSISDN: mobile systems integrated services data network number), onrequest from the data acquisition unit 47, which is arranged torecognise the card identities which require such translation. In apreferred embodiment the concordance is supplied to a register 43 in theground station by the operator of user's home network 7, when thenetwork operator provides the user with the card. The operator of thehome network 7 also records the concordance in its own Home LocationRegister 73. This arrangement allows the existing card readers 23 to beused on board the aircraft, without modification. If the users' mobilesubscriber identities are supplied from the onboard system, either byreading the identity (reader 311) or by the user keying it in, the store43 can be used for verification, or omitted. Billing information is alsoreturned to the user's home network 7.

The operation of the ground station 4 will now be described withreference to FIG. 6. The data acquisition unit 47 receives the carddetails from the reader 23 (see steps 601 to 604 already discussed) andif it identifies as those details as corresponding to a cellular user(step 605), it retrieves the cellular user identity from the store 43containing this concordance, or from the HLR 73 of the user's homenetwork, (step 606). (This step can be omitted if the user's mobilenetwork identity is provided by the onboard apparatus 20).

The data transmission unit 46 then generates a signal for transmissionof the cellular user identity, together with the identity of theterminal 21, to the cellular network 5 acting as host to the interface(step 607). This host network 5 will, in general, not be the same as theuser's home network 7. The further steps (608 to 615) in this processwill be described later, with reference to FIG. 5.

If a cancellation signal is received from the aircraft in respect of agiven terminal 21, (step 801, previously discussed) the datatransmission unit 46 transmits a “cancellation” signal to the hostnetwork 5. As already discussed, the cancellation signal may begenerated either for an individual handset 21, by its user dialling aspecial code, or for all handsets as the result signals received by theradio interface unit 28 over the aircraft's data bus 22 indicative ofthe imminent end of the flight.

An embodiment of the host network 5 of the invention is shown in FIG. 5.Its operation will be discussed with reference to FIGS. 6, 7 and 8 inthis network 5 an interface unit 52 is provided, which is arranged toappear to the switching system 50 as if it is a normal base station ofthe cellular radio system.

In order to do this, the interface unit 52 is provided with a dataacquisition unit 54 which receives from the card management system 42 ofthe ground station 4 the identity of the cellular telephone it is torepresent, and the AES identity of the onboard terminal 20 (step 608,FIG. 6). Mobile telephones have three identification codes: theequipment identity (IMEI, which will not be discussed further here), thedirectory number (MSISDN) and the actual SIM identity (IMSI). Inpractice, for security reasons, the IMSI is not made generally known,and a user is normally identified by his MSISDN unless the SIM itself isused. If the SIM is used in the card reader 23, or the user's telephoneis used in the arrangement of FIG. 3, (in which case no concordance isrequired) the IMSI can be read directly from the data received by thedata acquisition unit 54. However, if the user keys in his ownidentification data (step 603), or a concordance is provided by the cardreader 23, the data acquisition unit will receive the MSISDN, and notthe IMSI. (There may also be a PIN or other security code, which ischecked by the data acquisition unit 54).

In the GSM standard it is possible to obtain an IMSI from a known MSISDNby interrogating the appropriate Home Location Register 73. Thisembodiment makes use of the same facility to obtain the user identity ofthe originator, and then controls the location update process in respectof the user identity so obtained. To do this, the interface unit 52transmits a “request for routing information” signal, using the MSISDN(step 609). The standard HLR 73 responds to such a request with a signalwhich includes the IMSI corresponding to the MSISDN in the request (step610). (This “request for routing information” signal was provided underthe GSM standard as a means of obtaining routing information for datamessages intended for a destination for which only the MSISDN number isknown. However, it may be used for other purposes, such as thatdescribed above).

The telephone identity (IMSI), whether obtained directly from the cardreader 23 or handset 31, or indirectly as just described, is passed to anetwork registration unit 55 which exchanges signals with the mobileswitching centre 50 in the same way that a real cellular telephone woulddo. The mobile switching centre therefore informs the user's HomeLocation Register 73 that the mobile telephone is now registered withthe network 5 (step 611). The Home Location Register 73 records that themobile handset is now registered with host MSC 50 (step 612).

It should be noted that, although registered with the host MSC 50, theuser's mobile handset is not operatively connected to the host MSC 50—infact the mobile handset may be switched off to allow the card 24 to beused, or it may be connected to a user terminal 311. The user may be inan aircraft, anywhere in the world within the coverage area of thesatellite network.

The user's details, including any diversion instructions, are sent bythe Home Location Register 73 to the network's VLR 51 (step 613). Astore 57 records a copy of the details of these diversion instructions(step 614).

Conventionally, any incoming calls for a mobile user are sent in thefirst instance to the user's home network 7, and the HLR 73 providesinformation to identify the MSC 50 where the mobile handset cancurrently be found. Consequently, in the present arrangement, anyincoming calls intended for the mobile user will now by directed to thenetwork 5, as the mobile user is currently registered there.

The data acquisition unit 54 in the interface 52 now passes thedirectory number of the termination point 21 to a call diversioninstruction unit 56, which generates a “divert on busy” instruction tothe VLR 51 (step 615). This is a standard divert arrangement, andoperates such that should the mobile unit appear to be engaged onanother call when a call attempt is made to it, the call attempt isdiverted to a specified directory number, in this case the terminationpoint 21 or 21 a, identified by its AES code. This diversion instructionreplaces any previous instruction held in the VLR 51. Further settingsmay be made in the call diversion instruction unit 56, such as theidentification of a termination point 21 to which a data message is tobe sent when a call is diverted to another termination point 21 a.

Of course, there is in fact no mobile telephone connected to theinterface unit 52, and therefore it is unable to connect incoming callsto the mobile telephone in the conventional way, or to identify thecurrent true operating condition (switched off, busy, ready for calls,etc) of the mobile handset. Instead, the system responds to a callattempt as will now be described with reference to FIG. 7.

When a call attempt is made (step 701), the home MSC 70 to which thecall is initially routed obtains from the HLR 73 the current location ofthe mobile telephone (step 702), and on receiving the identity of thehost MSC 50 (step 703), directs the call there (step 703). The host MSC50 in turn transmits the call attempt to the currently serving basestation, which is in fact the interface unit 52 (step 704). If thedisconnect procedure (to be described later with reference to FIG. 8)has been carried out, the call will not be connected to the onboardsystem (step 705), and instead a signal is transmitted back to the homeMSC 70. Otherwise, call attempts received by the interface unit 52 arehandled by a call request handling unit 58, which automatically returnsa “busy” signal to any such request (step 706). The MSC 50, on receivingthe “busy” signal, retrieves the diversion information from the VLR 51(step 708) allowing it to route the call through the PSTN 8 to the userterminal 21, 21 a (step 710).

In the event that the destination terminal 21 a is not the terminal 21that originated the instruction, the call request handling unit 58 ofthe ground-based interface unit 52 may be arranged such that whenever amessage addressed to the user's MSISDN is diverted to the terminal 21 a,the call request handling unit 58 also generates a data message (step711) for transmission to the instructing terminal 21 by way of the MSC50, PSTN 8, and satellite system 4, 6 (step 712) either during the callor after it ends. Such a message can be used for example to alert theuser of the terminal 21 that a facsimile message addressed to him hasbeen sent to the terminal 21 a. As with the call alerting processdescribed above, the message may be displayed using the in flightentertainment system 200.

If a second call attempt is made, the ACSE 40 may identify that thedivert instruction will not work as it is currently handling a divertedcall to that number. The default condition in such cases is to arrangefor the second call to be diverted to the user's voicemail address (notshown) in his home network 7. The user may also be sent a data messageto inform him of the new voicemail message. This message would normallybe sent to the mobile unit, which appears to the MSC 50 to beco-operating with the interface unit 52, so the MSC 50 transmits thedata message to the interface unit 52 (step 711). In order to inform theuser of the new voice mail message, the interface unit 52 nowregenerates the data message for forwarding to the user terminal 21 viathe MSC 50, PSTN 8, and satellite system 4, 6 (step 712) either duringthe call or after it ends. However, data messages are not suitable forswitching via the MSC 50 and PSTN 8, nor for handling by the on-boardterminal 21 as it is only equipped for voice. A method for transmittingdata messages over this interface will be described later, withreference to FIGS. 9 and 10.

Generally, the detection of the same IMSI from two sources causes an HLRto disconnect both callers as a fraud prevention measure. Since thissystem causes the generation of an IMSI from the interface unit 52,instead of directly from the mobile telephone to which that IMSIrelates, the user's mobile telephone should be switched off, orconnected to an onboard interface device 311 which disconnects the radiocircuits, to prevent the network detecting the IMSI in two places, whichwould disrupt the call routing processes in the HLR 73 and elsewhere. Ifthe user is on board an aircraft, he should not be using his mobilehandset in the conventional manner, and so there should be no problem.However, if the user, having left the aircraft, switches on histelephone 75 before the network 5 has reported a loss of the mobile unitfrom its own network, the mobile unit may be perceived by the HLR 73 asbeing registered with two networks at once. To avoid this possibility, adisconnection procedure is followed as described with reference to FIG.8.

As already discussed, to stop calls being diverted to the usertermination point 21, and restore the original call diversion settings,a disconnection signal may be transmitted from the onboard system 28 tothe host network's interface unit 52 (step 801). The disconnectionsignal may be activated by a special code entered by the user, or it maybe generated automatically by data collected from the aircraft's databus 22 indicative of the imminent end of the flight. Note that thisdisconnection signal merely controls the interface 52—it has no effecton calls in progress, which is routed from the host MSC 50 by way of thePSTN 8.

The disconnect instruction is received by the interface unit 52 (step802) and causes the call diversion instruction unit 56 to retrieve thecall diversion data stored in the store 57 (step 803) and generate acall diversion instruction restoring the original settings to the VLR 51(step 804). This ensures no further calls are routed to the onboardterminal 21.

The interface unit 52 next causes the network registration unit 55 inthe interface unit 5 to instruct the MSC 50 that the user is no longerconnected to the network 5 (step 805). This allows the mobile unit toregister with another network 7 in the normal way. Call attempts to theuser number will continue to be routed by the Home HLR 73 to the MSC 50with which the mobile unit was most recently registered, (i.e. the hostMSC 50) but as that MSC cannot now find the mobile unit, any suchincoming call will return a “not found” signal to the home MSC 70 whichwill divert the call according to any diversion instructions set up, orfail the call. Alternatively, the host MSC 50 may handle the diversionitself if the mobile unit is “not found”, using the original diversioninstructions now in the VLR 51, having been retrieved from the store 57(step 804 above).

Having left the aircraft, the user may switch on his mobile telephone75, which will register with the local network (e.g. 7) and willretrieve the original divert information from the HLR 73 (note that ingeneral the HLR 73 will not be in the same network), and will cause alldata relating to the user to be deleted from the VLR 51 in the “host”network 5.

Because the IMSI is recorded in the HLR 73 as being registered with the“Virtual” BSC, or interface unit, 52, any other data messages intendedfor the user will also be routed to the interface unit 52, and requireforwarding to the user. As with the call alerting process describedabove, the message may be displayed using the in flight entertainmentsystem 200.

An alternative embodiment, in which voice calls are handled by a user'scellular handset but data calls and call alerts are still handled by theonboard in-flight entertainment system, is depicted in FIGS. 11 and 12.

The system can be categorised into two main components: namely theonboard part 101 (FIG. 11) and the fixed part 102 (FIG. 12), whichcommunicate with each other through a satellite connection 6. Theonboard part (FIG. 11) comprises a moveable cellular system111,112,114,116 and the onboard part 113 of the tracking radio system.The fixed part 102 (FIG. 12) is itself in two parts, namely a satelliteground station 4, which is similar to that shown in FIG. 1 and the fixed“host” cellular network 104, which is a public land mobile network(PLMN), in turn interconnected with other PLMNs 70 and conventionalwired networks (PSTN) 8 to allow calls to be made between users ofdifferent networks.

As shown in FIG. 11, the system provides a cellular radio subscriberwith the ability to use his own handset 110 aboard an aircraft, locatedanywhere within an agreed satellite coverage area. The coverage on boardthe aircraft can be provided by any suitable means, using known radiorepeater distributions systems 111 to provide radio coverage whereverrequired.

The distribution system 111 is fed by a base transceiver site 112,served by a base site controller 114 and a mobile switching centre 116,which may have its own visitor location register 117, for onwardtransmission to the satellite ground station 4 via a satellite trackingsystem 113. The satellite tracking system may be a conventionalsatellite telephone system as commonly used for ship-to-shorecommunications, and for the airborne systems previously referred to,providing a satellite link 6 from the aircraft or ship's satellitetracking system 113 to the satellite ground station 4. The satelliteground station 4 is in turn connected to the mobile switching centre(MSC) 141 of a conventional cellular telephone system, referred tohereinafter as the “host” system 104 and shown in FIG. 12.

The satellite link 4-6-113 is therefore between the onboard MSC 116 andan MSC 141 (the “host” MSC) of the land-fixed “host” network 104. Theuser record in the home location register (HLR) 73 of the user's homenetwork identifies the mobile unit 110 as currently served by the hostnetwork 104, and routes the call to the host MSC 141, which will in turnrecognise from its entry in the land based VLR 144 that this mobile unitis currently being served by the onboard MSC 116. The way this isarranged will be described later.

This arrangement allows integration of the onboard MSC 116 with theonboard switching capability associated with the conventional satellitetelephone system and the aircraft's internal communications system 115.In particular it provides a simple means of providing passengers andcrew with a “Wireless PBX” facility, as users on board the aircraft cancommunicate with each other through the BSC 114 without using thesatellite link 4-6-113. When a call is made by a cellular telephone 110,the onboard MSC 116 first consults its VLR 117 to establish whether thecalled party is currently served by the same MSC 116. If this is thecase, it connects the call without the use of any inter-MSC links. Thuscalls made between two users both on board the aircraft 101 may be madewithout the use of the satellite link 4-6-113. The satellite connectionprovides several voice channels and a signalling channel (supervisorycontrol-management channel), and can be made by any connection ofappropriate capacity.

The host network 104 may support one or more further base sitecontrollers 142 controlling conventional base transceiver sites 74. Thehost Mobile Switching Centre 141 also has an associated “VisitorLocation Register” 144 which, in conventional manner, records details ofthe cellular telephones currently co-operating with the Mobile SwitchingCentre 141, so that details can be exchanged with the Home LocationRegister 73 of the user's home network for billing purposes, and toallow incoming calls to be routed correctly. These details include theidentity of the link 4, 142 to which the user is connected, allowingdifferent call charges to be applied for use in different cells, and inparticular to distinguish between calls made through the onboard basetransceiver site 112 and calls made through conventional base sitecontrollers 142.

In the cellular mobile network 104, standard GSM functionality is used.Users aboard the aircraft will be able to use this service provided theyare subscribers to the host network 104, or any other network 70 whichhas a “roaming” agreement with the host network 104, provided thesubscriber has the roaming capability authorised by his serviceprovider.

In this embodiment of the invention, the “host” network 104 operateslike a conventional cellular network, but is provided with an interfaceunit 148 for interworking with the satellite ground station 4. Thisinterface 148 allows the switching centre 141 to obtain user details (inparticular the identity of a mobile handset) from the satellite system 4to allow it to appear to the network 104, and thus to the HLR 73 in theuser's home network, that the mobile handset is in radio communicationwith a base station under the control of the mobile switching centre 141when in fact it is in communication with the onboard MSC 116. The mobileswitching centre can then arrange for call forwarding instructions to bestored in the VLR 144, to cause incoming calls directed to that handsetto be diverted, through the switching system 40 of the satellite network4, to the onboard MSC 116.

The operation of the system is as follows. When a mobile unit 110 firstmakes contact with the onboard cellular system 101 it transmits itsidentity code (IMSI) to the onboard MSC 116 in the usual way. Theonboard MSC 116 can obtain verification data from the user's HLR 73(identified by the IMSI code) to verify the authenticity of the user,and permit outgoing calls. However, because the onboard MSC 116 is onlycontactable through the satellite system, incoming calls to the mobileunit 110 cannot be reliably routed to the onboard MSC 116 over aconventional link. In order to avoid a requirement for specialfacilities in each network 70 it is convenient to make the mobile unit110 appear to be working to a conventional mobile switching centre 141.

When the onboard MSC 116 detects a call attempt or registration attemptfrom a mobile unit 110, it collects from the mobile unit its identitycode (IMSI) and passes it to a processor 118. If the processor 118 hasnot previously done so, it generates a temporary onboard identity forassociation with the mobile identity code (IMSI), and stores it in amemory 119. For aircraft fitted with at-seat satellite telephoneequipment, each handset has an identity code (generally related to thenumber of the passenger seat to which the handset is fitted) to allowoutgoing calls to be billed to the correct user and to allow the systemto be used to communicate between passengers. Spare numbers in thissystem (referred to herein as “pseudo seat numbers”—PSN) may be used asthe temporary onboard identities allocated to mobile handsets working tothe onboard MSC 116. If the mobile handset 110 has previously contactedthe onboard MSC 116, and not subsequently de-registered, the processor118 now retrieves the PSN corresponding to the IMSI from the memory 119.

As with the arrangement of FIG. 1, the present embodiment allows thehost network to translate the called party's IMSI to an AES code(including seat number), which in this case is a pseudo-seat number(PSN) allocated randomly from the numbers left spare after codes havebeen allocated for at-seat terminals. The translation takes place in thehost network, without the need for the caller to know the AES code. Thetemporary onboard identity code PSN associated with the called party'sIMSI is returned to the onboard MSC 116 which sets up a call over thesatellite system to the host MSC 141 of the host network 104. Thesatellite system requires certain authentication data on call set up,namely the AES code and a subscriber identity code which normallyidentifies an individual subscriber to the satellite system or, if theuser does not have an account with the satellite system, credit carddetails or other details to allow payment to be made. In the presentcase the onboard MSC 116 provides the cellular telephone's code (IMSI)as the subscriber identity code. For security reasons, this code may beencrypted. If an outgoing call attempt is being made, a call attempt isthen made to the number dialled; otherwise a special code, referred toherein as the non-call code (“NCC”) is used.

If the caller has not previously been registered, but a special non-callregistration code is used, the ACSE 40 of the ground station 4recognises it as being an authorised free call to the host MSC 141 androutes it accordingly. Calls using this code are permitted even if theIMSI has not previously been registered with it.

The host network 104 will, in general, not be the same as the user'shome network 70. In the host network 104 the interface unit 148 providescertain additional functionality to co-operate with the satellite groundstation 4.

When a call is received by the satellite ground station 4 using thenon-call code (NCC) the ACSE 40 retrieves the data and passes it to aninterface unit 148, which retrieves the identity (IMSI) of the cellulartelephone, and the PSN associated with it. The IMSI (de-encrypted ifnecessary), is passed to a network registration unit 145 which exchangessignals with the host mobile switching centre 141 in the same way that areal cellular telephone would do if registering through one of its basestations 74. The mobile switching centre therefore informs the user'sHome Location Register 73 that the mobile telephone is now registeredwith the network 104. The Home Location Register 73 records that themobile handset is now registered with host MSC 141.

It should be noted that, although registered with the host MSC 141, theuser's mobile handset is not operatively connected to the host MSC 141.The user, and the handset, may be on a suitably equipped vehicleanywhere in the world within the coverage area of the satellite network6.

The user's details, including any diversion instructions, are next sentby the Home Location Register 73 to the network's VLR 144. A store 147records a copy of the details of these diversion instructions forsubsequent retrieval when the mobile unit deregisters.

Conventionally, any incoming calls for a mobile user are sent in thefirst instance to the user's home network 70, and the HLR 73 providesinformation to identify the MSC where the mobile handset is expected tobe found, which is the host MSC 141. Consequently, in the presentarrangement, any incoming calls intended for the mobile user will now bedirected to the network 104, as the mobile user is currently registeredthere.

The interface unit 148 passes the AES code to a call diversioninstruction unit 146, which generates a “divert on busy” instruction tothe VLR 144. This is a standard divert arrangement, and operates suchthat should the mobile unit appear to be already engaged on a call whena new call attempt is made to it, the new call attempt is diverted to aspecified directory number, in this case the AES code allocated to themobile unit. This diversion instruction replaces any previousinstruction held in the VLR 144.

Finally, the registration process is closed by returning anauthorisation code from the host MSC 141 to the subscriber managementsystem 42 of the satellite system 4, to allow the IMSI to be recognisedas a valid user identification for subsequent outgoing calls.

The aircraft may have an at seat information system 200 with provisionfor connection of the handset 110, similar to the hands-free setscommonly provided in cars. This allows audio signals to be transferredto the at-seat system's headset 202, preventing disturbance to otherpassengers. The at-seat system may also have means for collectingringing tone from the handset 110, and generating a visual alert on thedisplay screen 201 or an audible one on the headset 202.

The operation of the system will now be described with reference to FIG.13. When a mobile unit 110 first makes contact with the onboard cellularsystem 101 it transmits its identity code (IMSI) to the onboard MSC 116in the usual way. The onboard MSC 116 can obtain verification data fromthe user's HLR 73 (identified by the IMSI code) to verify theauthenticity of the user, and permit outgoing calls. However, becausethe onboard MSC 116 is only contactable through the satellite system,incoming calls to the mobile unit 110 cannot be reliably routed to theonboard MSC 116 over a conventional link. In order to avoid arequirement for special facilities in each network 70 it is convenientto make the mobile unit 110 appear to be working to a conventionalmobile switching centre 141.

When the onboard MSC 116 detects a call attempt or registration attemptfrom a mobile unit 110, (step 1601) it collects from the mobile unit itsidentity code (IMSI) and passes it to a processor 118. If the processor118 has not previously done so, it generates a temporary onboardidentity for association with the mobile identity code (IMSI), andstores it in the memory 119 (step 1602). For aircraft fitted withat-seat satellite telephone equipment, each handset has an identity code(generally related to the number of the passenger seat to which thehandset is fitted) to allow outgoing calls to be billed to the correctuser and to allow the system to be used to communicate betweenpassengers. Spare numbers in this system (referred to herein as “pseudoseat numbers”—PSN) may be used as the temporary onboard identitiesallocated to mobile handsets working to the onboard MSC 116. If themobile handset 110 has previously contacted the onboard MSC 116, and notsubsequently de-registered, the processor 118 retrieves the PSNcorresponding to the IMSI from the memory 119 (step 1603).

In existing onboard systems a user cannot receive calls unless thecaller knows the unique “AES” number of the at-seat terminal 201, whichis made up of the seat code and an identity code of the aircraft (whichtogether make up a unique “AES” code). It is unlikely, even for a normalsatellite handset, that a caller would know the AES code, as the numberdepends on the identity of the aircraft, the seat, and the servingsatellite or base station. (It should be noted that the passenger listof an aircraft is not normally released to the general public until theflight has ended, for security reasons). The present embodiment allowsthe host network to translate the called party's IMSI to an AES code,which includes a pseudo-seat number (PSN), which is allocated randomlyfrom the numbers left spare after codes have been allocated for at-seatterminals. The translation takes place in the host network, without theneed for the caller to know the AES code.

The temporary onboard identity code PSN associated with the calledparty's IMSI is returned to the onboard MSC 116 which sets up a callover the satellite system to the host MSC 141 of the host network 104(step 1604). For a normal satellite call, the satellite system requirescertain authentication data on call set up, namely the AES code and asubscriber identity code which normally identifies an individualsubscriber to the satellite system or, if the user does not have anaccount with the satellite system, credit card details or other detailsto allow payment to be made. In the present case the onboard MSC 116provides the cellular telephone's code (IMSI) as the subscriber identitycode. For security reasons, this code may be encrypted. If an ongoingcall attempt is being made, a call attempt is then made to the numberdialled; otherwise a special code, referred to herein as the non-callcode (“NCC”) is used.

The satellite ground station 4 is similar to that shown in FIG. 4, andhas a radio antenna system 44 for communicating with the onboard system101, through a satellite link 6 or otherwise. Signals are handled by anAccess Control Signalling Equipment (ACSE) 40 which carries outswitching functions to route calls to or from the public switchedtelephone network (PSTN) 8.

A subscriber management system 42 in the satellite ground stationcomprises a data acquisition unit 47 which reads identification datatransmitted from the aircraft (step 1605) to identify the subscriber,confirm his account details and arrange billing for any calls made,through a billing system 45 which raises invoices, or interacts with thesystems of a credit card operator, bank, or other telephone operator. Inthe present case the card management system recognises the IMSItransmitted as the subscriber identity. Provided the IMSI has previouslybeen registered with the subscriber management system 42 (as willshortly be described: step 1616) the call is authorised using thesatellite system's authorisation checking and billing system as for anycall from an onboard satellite terminal, and connected to the PSTN 8(step 1606), billing details being passed to the home network throughthe host MSC 41.

If the caller has not previously been registered, but a special non-callregistration code is used, the ACSE 40 recognises it as being anauthorised free call to the host MSC 141 and processes it accordingly(step 1607) by retrieving the data and forwarding it to the interfaceunit 52 in the host network 5. Calls using this code are permitted bythe subscriber management system 42 even if the IMSI has not previouslybeen registered with it.

The host network 104 will, in general, not be the same as the user'shome network 70. In the host network an interface unit 148 providescertain additional functionality to co-operate with the satellite groundstation 4.

An aircraft location register 41 associated with the interface unit 148stores identification details for all aircraft 101 currently served byeach satellite ground station 4. When an aircraft passes into thecontrol of a different satellite the aircraft location register isupdated accordingly.

When a call is received from the satellite ground state 4 using thenon-call code (NCC) the ACSE 40 transmits the data to the interface unit148 (step 1608). The interface unit 48 then retrieves the identity(IMSI) of the cellular telephone, and the AES identity of the onboardterminal 201 (step 1608, FIG. 13). The IMSI (de-encrypted if necessary),is passed to the network registration unit 145 which exchanges signalswith the host mobile switching centre 141 in the same way that a realcellular telephone would do if registering through one of its basestations 74. The mobile switching centre therefore informs the user'sHome Location Register 73 that the mobile telephone is now registeredwith the network 104 (step 1611). The Home Location Register 73 recordsthat the mobile handset is now registered with host MSC 141 (step 1612).

It should be noted that, although registered with the host MSC 141, theuser's mobile handset is not operatively connected to the host MSC 141.The user, and the handset, may be on a suitably equipped vehicleanywhere in the world within the coverage area of the satellite network6.

The user's details, including any diversion instructions, are next sentby the Home Location Register 73 to the host network's VLR 144 (step1613). A store 147 records a copy of the details of these diversioninstructions (step 1614).

Conventionally, any incoming calls for a mobile user are sent in thefirst instance to the user's home network 70, and the HLR 73 providesinformation to identify the MSC where the mobile handset is expected tobe found, which is the host MSC 141. Consequently, in the presentarrangement, any incoming calls intended for the mobile user will now bedirected to the host network 104, as the mobile user is currentlyregistered there.

The interface unit 148 passes the AES code to a call diversioninstruction unit 46, which generates a “divert on busy” instruction tothe VLR 144 (step 1615). This is a standard divert arrangement, andoperates such that should the mobile unit appear to be already engagedon a call when a new call attempt is made to it, the new call attempt isdiverted to a specified directory number, in this case the AES codeallocated to the mobile unit. This diversion instruction replaces anyprevious instruction held in the VLR 144.

Finally, the registration process is closed by returning anauthorisation code from the host MSC 141 to the subscriber managementsystem 42 (step 1616) to allow the IMSI to be recognised as a valid useridentification for subsequent outgoing calls.

Of course, although the mobile telephone 110 is recorded in the homelocation register 73 and in the host's visitor location register 144 asbeing connected to the host MSC 141, it is not really there andtherefore the host MSC 141 is unable to connect incoming calls to themobile telephone in the conventional way, or to identify the currenttrue operating condition (switched off, busy, ready for calls, etc) ofthe mobile handset 110. Instead, the system responds to a call attemptas will now be described with reference to FIG. 14.

When a call attempt is made (step 1701), the MSC in the home network 70to which the call is initially routed obtains from the HLR 73 thecurrent location of the mobile telephone (step 1702), and on receivingthe identity of the host MSC 141, directs the call there (step 1703).The host MSC 141 in turn attempts to transmit the call attempt to thecurrently serving base station, which is in fact the interface unit 148(step 1704). If the disconnect procedure already described withreference to FIG. 8) has been carried out, the call will not beconnected (step 1705) and a signal is transmitted back to the home MSC70. Otherwise, the interface unit 148 automatically returns a “busy”signal to any such request (step 1706). Note that the interface unit 148has no information regarding the true operating state of the mobile unit110. It is merely arranged to emulate the target mobile unit's responseto a call attempt when the target mobile unit is in the “busy”condition.

The host MSC 141, on receiving the “busy” signal, checks whether anyincoming call currently in progress to that mobile handset has alreadybeen diverted (step 1707). (This is a standard procedure, done to ensurethat call diversions are not attempted if they will not actuallysucceed). If there is no such diverted call in progress, the host MSC141 retrieves the diversion information (the AES) from the VLR 144 (step1708) allowing it to route the call through the PSTN 8 and the satellitesystem 4-6-113 to the onboard system 101 (step 1710).

The onboard system 101 routes incoming calls to a node of the onboardsystem according to the AES code. If the node is connected to a realat-seat terminal, the call is simply routed to that terminal. However,in this case, the code corresponds to a pseudo seat number, which theonboard satellite system switch 113 recognises as meaning that the callis to be routed to a node connected to the onboard MSC 116. The onboardMSC 116 uses the processor 118 to retrieve from the memory 119 thecellular identity (IMSI) corresponding to the PSN, (step 1711) and thenconnects the call to the mobile handset 110 having that identity in theconventional manner (step 1712). Thus the interaction between theonboard MSC 116 and the handset 110 is entirely conventional: ordinaryhandsets can be used and no initial authorisation is required other thanthe standard procedure used to ensure that international “roaming” ispermitted.

If a second call attempt is made to a handset already in use, the ACSE50 will identify that the divert instruction will not work as it isalready handling a diverted call to that number. The default conditionin such cases is to arrange for the second call to be diverted to theuser's voicemail address (not shown) in his home network 70. The usermay also be sent a message to inform him of the new voicemail message.This message would normally be sent to the mobile unit, which appears tothe host MSC 141 to be co-operating with the interface unit 148, so thehost MSC 141 transmits the data message to the interface unit 148 (step1711). In order to inform the user of the new voice mail message, theinterface unit 148 now regenerates the data message for forwarding tothe onboard MSC 116 via the satellite system 3 (step 1712) for alertingthe user terminal 110 either during the call or after it ends.

As the onboard system 101 is itself mobile, being on board an aircraft,call routing to that termination may require revision from time to time.For example, the “Inmarsat” satellite system comprises severalgeostationary satellites, which each provide cover for part of theearth's surface. These areas of coverage overlap to a large extent, butnevertheless on a long flight the aircraft may pass out of the areacovered by one satellite into that served by another. This causes asmall but significant change in the network address AES of any terminalon board the aircraft. The aircraft location register 41 monitors theidentity of all aircraft currently being handled by the satellite groundstation 4. When an aircraft moves into range of a different satellite 6,the call diversion unit 146 responds by transmitting a new calldiversion instruction to the VLR 144, so that any further incoming callattempts are diverted to the new network address (AES) of the nodecorresponding to the terminal 110. Note that the diversion store 147 isnot updated.

Note also that this does not affect calls already in progress. There isusually sufficient overlap in satellite coverage areas that handoverfrom one satellite or base station to another can be arranged to takeplace when no call is in progress.

During the flight the user may decide that he no longer wishes to havehis calls diverted to the terminal 110, and switches it off. The onboardMSC 116 will therefore fail to locate the mobile handset 110 at the nextregistration update. As previously discussed, it is also desirable todisable the onboard system 101 when the aircraft is on approach tolanding, to avoid interference with aircraft systems at this criticalpoint in the flight (or distractions to passengers in the event of anemergency), and also to avoid interference with base stations on theground. Disconnect codes may therefore be generated in the onboard MSC116 for all the handsets 110, either by the cabin crew or automaticallyin response to a signal detected on the aircraft's data bus 22 which isindicative of the imminent end of the journey, such as time remaining todestination (as determined by the aircraft's flight management system),low altitude, deployment of undercarriage, or weight on wheels.

The deregistration process of this embodiment is similar to that of thefirst embodiment. On receiving a de-registration signal (steps 801,802FIG. 8), the host network 104 retrieves the original divert informationfrom the store 147 (step 803) and stores that in the VLR 144 (step 804),thereby restoring the user's own selected divert instructionsautomatically.

Once he has left the aircraft, the user may switch on his mobiletelephone 110, which will register with the local network (e.g. network70), informing the home location register 73 of the location update(note that in general the HLR 73 will not be in the same network as thelocal network 70). The HLR 73 retrieves the user's VLR settings from theprevious host network 102. Because the original VLR data has beenrestored (step 804), the temporary divert data used whilst the user wasconnected to the onboard system is not fed back to the HLR. All datarelating to the user can then be deleted from the VLR 44 in the “host”network 102 (step 805).

In use, both parties to a call, and most of the cellular network,operate normally. The cellular telephone 110 co-operates with the basestation 112 on the aircraft as it would with any other base station 74.The home location register 73 identifies the cellular telephone 110 ascurrently served by the host MSC 141, and routes incoming callsaccordingly. This embodiment therefore allows connection to be made toconventional handsets 110 using standard cellular telephony equipment.The operation of the host MSC 141 and the onboard MSC 116 are bothlargely conventional except for the number translation functions carriedout by the interface units 118, 148. Using roaming capabilities, justone host MSC 141 can provide connection to a large number of airborneMSCs 116, anywhere in the range of the satellite system 4, 6.

To allow the use of the at seat display system 201 for data messages,not suitable for transmission over the PSTN and satellite system intheir original form the interface unit 52 (FIG. 5), 148 (FIG. 12) isprovided with a data handling processor 53,149 for receiving datamessages received over a packet data system 9 by way of the MSC 50,141and intended for users currently associated with the interface unit52,148. These messages include SMS messages sent from other callers, andSMS messages generated by the MSC 50,141 itself to alert the user that amessage has been sent to the voice mail system. The format of such amessage is shown in FIG. 9, and the process of sending and receiving itis shown in FIG. 10.

The original message 900 basically consists of a data payload 901 and anaddress 902, which is the IMSI of the destination mobile telephone (FIG.9 a).

When the interface unit 53,148 receives such a data message (step 990)it retrieves from the data acquisition unit 54,149 the data networkaddress of the at-seat entertainment terminal 201 corresponding to theuser's cellular identity which was originally provided to the dataacquisition unit 54,149 when the user carried out the registrationprocedure (step 991). The interface unit 53,148 next generates a datacall to that address (step 992), in a form suitable for transmission bythe MSC 50,141 (step 993) over the packet data network 9 to theaircraft, with an address header corresponding to the data networkaddress of the user's at-seat terminal 201,201. This data call may be ashort message to indicate that a message is awaiting delivery, anddisplaying on the screen 201 an invitation to the user to dial a specialcode on his handset 25,110 to accept the message (step 994), and anycharge associated with it. This acceptance is transmitted back, by wayof the MSC 50, 141 to the interface unit 53,148 (step 995). (These steps992-995 may be omitted if it is not required for users to acknowledgeacceptance before receiving a data message).

The interface unit 53,148 then replaces the address header (the IMSI)902 in the original data message with a code 912 identifying theterminal 201 and encapsulates the message in a form suitable fortransmission over the packet data network 9 to the aircraft (step (996),with an address header 910 to send it to the data network interface 28,204 serving the onboard entertainment system 200. It can thus betransmitted to the interface 28, 204 over the packet data network 9(step 997), effectively as a packet with an address header 910 and apayload made up of the at-seat terminal number 912 and true payload 901(FIG. 9 b).

On receipt of the data message, the on board data interface 28, 204extracts the data message payload 901, 912, (FIG. 9 c) (step 998) andidentifies the individual at-seat terminal 201 identified by the address912. It can then cause display of the data message payload 901 on thescreen 201 of the appropriate terminal (step 999).

If password protection is required, for example to ensure that the useris present when the message is displayed, the payload 901, 912 can alsoinclude a password code 913, which causes the interface 28, 204 towithhold the remainder of the payload until a predetermined sequence ofkeystrokes has been entered by the user in the terminal 201.

In the embodiment of FIGS. 11 and 12 the invitation (step 992) may besent as a voice message to the user terminal 110, and prompts the userto identify his at-seat terminal (in practice the user will be asked forthis seat number), either by key presses (using DTMF coding) or by voice(step 995). The acceptance step is therefore performed over the voicenetwork, rather than the data network. The MSC 141 uses this informationto generate an AES code identifying the user terminal, to be applied tothe data message 910 (FIG. 9). The host MSC may store this code for usewith subsequent data messages, allowing the host MSC 141 to processfurther data messages without requesting this information from the useragain. The request for the user's seat number may instead be made whenhe first registers his telephone 110 with the onboard MSC 116.

As the terminal is itself mobile, being on board an aircraft, callrouting to that termination may require revision from time to time. Forexample, the “Inmarsat” satellite system comprises several geostationarysatellites, which each provide cover for part of the earth's surface.These areas of coverage overlap to a large extent, but nevertheless on along flight the aircraft may pass out of the area covered by onesatellite into that served by another. This causes a small butsignificant change in the network address of any satellite terminal onboard the aircraft. The aircraft location register 41 monitors theidentity of all aircraft currently being handled by the ground station4. When it an aircraft location is updated, it sends an updatinginstruction to the interface unit 52, 148. The call diversioninstruction unit 56, 146 responds by transmitting a new call diversioninstruction to the VLR 51,144 so that any further incoming call attemptsare diverted to the new network address of the terminal. Note that thediversion store 57,147 is not updated. Note also that this does notaffect calls already in progress: there is usually sufficient overlap incoverage areas that handover from one satellite or base station toanother can be arranged to take place when no call is in progress.

Three further embodiments of the invention will now be described, by wayof example, with reference to FIGS. 15 to 17 of the drawingsrespectively. These embodiments are all based on the system architectureof the GSM (Global System for Mobile radio) standard, and are intendedfor use on board a ship. These embodiments differ in the location of thevarious components of the GSM system architecture, and the position ofthe satellite link in that architecture.

In all three embodiments, the system can be categorised into two maincomponents: namely the shipboard part 501 and the fixed part 502,communicating with each other through a satellite connection 6. Thefixed part 502 is itself in two parts, namely a satellite earth station4 and a public land mobile network (PLMN) 504, which is in turninterconnected with other mobile networks 7 and fixed networks 5 toallow calls to be made between users of different networks.

The system provides a cellular radio subscriber with the ability to usehis own handset 510 aboard a ship, located anywhere within an agreedsatellite coverage area. The coverage aboard ship can be provided by anysuitable means, using known radio repeater distribution systems 511 toprovide radio coverage wherever required. The arrangement of FIG. 15will be described first.

The distribution system 511 is fed by a base transceiver site 512, foronward transmission to the satellite earth station 4 via a satellitetracking system 513. The satellite tracking system may be a conventionalsatellite telephone system as commonly used for ship-to-shorecommunications, providing a satellite link 6 from the ship's satellitetracking system 513 to the satellite earth station 4. In the embodimentof FIG. 15, the satellite earth station 4 is in turn connected to a BaseSite Controller (BSC) 540 associated with the mobile switching centre(MSC) 541 of a conventional cellular telephone system. The satelliteconnection provides several voice channels and a signalling channel(supervisor control—management channel), and can be made by anyconnection of appropriate capacity.

In the cellular mobile network 504, standard GSM functionality is used.Both the base transceiver site 512 and the shore-based base sitecontroller 540 are largely conventional, but have an extra softwareupload facility to allow for the delays incurred over the satellite link4-6-513. In particular the “A-bis” link between a BTS and a BSC normallyhas an allowable time delay of 40 ms. Longer delays are identified asbeing indicative of a fault and a cause the link to be shut down. Inthis embodiment the allowable delay is expanded to approximately 700 msto allow for delays in the satellite link 4, 6, 513. The base sitecontroller 540 operates in conventional manner, being connected to themobile switching centre 541 of the host network 504. The host network504 may also support one or more further base site controllers 542controlling conventional base transceiver sites 74. The Mobile SwitchingCentre 541 also has an associated “Visitor Location Register” 544 which,in conventional manner, records details of the cellular telephonescurrently co-operating with the Mobile Switching Centre 541, so thatdetails can be exchanged with the Home Location Register 73 of theuser's home network for billing purposes, and to allow incoming calls tothe handset 510 to be routed correctly. These details include theidentity of the BSC 540, 542 to which the user is connected, allowingdifferent call charges to be applied for use in different cells, and inparticular for calls made through the onboard base transceiver site 512.

Users aboard the ship will be able to use this service provided they aresubscribers to the host network 504, or if they subscribe to a network 7which has a “roaming” agreement with the host network 504, and thesubscriber has global roaming authorised by his service provider.“Roaming” is the arrangement which allows a subscriber to one network touse his cellular telephone when connected to another network.

In use, both parties to a call, and the cellular network, operatenormally. The cellular telephone 510 co-operates with the base station512 on the ship as it would with any other base station 74. The homelocation register 73 identifies the cellular telephone 510 as currentlyserved by the MSC 541, and routes incoming calls accordingly.

In the variant of this embodiment shown in FIG. 16, the Base SiteController 514 is on the ship, and the satellite link 4-6-513 is betweenthe MSC 541 and the BSC 514. This reduces the signalling overhead overthe satellite link 4-6-513 as there is much less traffic between an MSCand a BSC than there is between a BSC and a BTS, so the cost of thesatellite link can be reduced—perhaps to the extent that an on-demandsatellite link may be preferable to a permanently leased one. Despiteits onboard physical location, the BSC 514 is still perceived by thenetwork 504 as part of the region served by the MSC 541.

In the third embodiment, shown in FIG. 17, a subsidiary mobile switchingcentre 516 is provided on board the ship, with its own visitor locationregister 517. The satellite link 4-6-513 is now between the shore basedMSC 541 and the onboard MSC 516. The user record in the HLR 73 willidentify the mobile unit 510 as currently served by the onboard MSC 516,and route incoming calls (by way of the shore based MSC 541)accordingly. Alternatively, the HLR may merely identify the mobile unit510 as served by the network 504, and route the call to the MSC 541,which will in turn recognise from its entry in the shore based VLR 544that this mobile unit is currently being served by the subsidiary MSC516.

This embodiment allows integration of the onboard MSC 516 with theship's internal telephone exchange (PBX) 515. In particular it providesa simple means of providing passengers and crew with a “Wireless PBX”facility, as users on board the ship can communicate with each otherthrough the BSC 514 without using the satellite link 4-6-513. When acall is made by a cellular telephone 510, the serving MSC 516 firstconsults its VLR 517 to establish whether the called party is currentlyserved by the same MSC 516. If this is the case, it connects the callwithout the use of any inter-MSC links. Thus, in this third embodiment,calls made between two users both on board the ship 501 may be madewithout the use of the satellite link 4-6-513.

If the ship 501 moves into radio range of land-based base transceiversites 74, signals from the land-based sites may interfere with theonboard transceivers 511, and vice versa. It is known for conventionalland-based systems to experience similar problems from time to time as aresult of variations in atmospheric conditions, or other factorsaffecting radio propagation such as temporary structures in the line ofsight, or even whether trees are in leaf. Such land based systems can bearranged to select alternative frequencies or reduce signal strength ifsuch interference is detected. However, the situation with a mobile basestation 511 is more complex. In particular, the mobile base station willnot, in general, have a license to operate within the territory coveredby the fixed base stations 74, and may only be permitted to operate in,and be detectable in, international waters. This means that the systemshould be shut down when in territorial waters, so that users on boardcan operate with the local land-based system 74. Moreover, the powershould be controlled so that if the mobile base stations are close tothe boundary T of territorial waters, other mobile users withinterritorial waters will nevertheless connect to a land-based station.

FIG. 18 illustrates a typical situation. The system will be assumed tooperate according to the general arrangement of FIG. 16: that is thesatellite link 4, 6, 513 is between the base site controller 514 and themobile switching centre 541.

The ship 501 is outside territorial waters (boundary T) and there is aterrestrial base station 74 on the shore. The lower part of the diagramillustrates how the power output of an above-deck base station 511 iscontrolled at two locations 511 a, (power received represented by fullline) and 511 b (power in dotted line) such that, in both cases, withinthe boundary T the received power is so low that a cellular telephonewill not be able to register with it. The position of the boundary Trelative to the ship 501 can be determined using any known navigationsystem such as the satellite-based “Global Positioning System”, using aGPS satellite 591 and receiver 590, linked to a database determiningwhere such boundaries T are located.

To avoid interference with other radio systems outside territorialwaters, and to prevent users in nearby vessels using the onboard system511 in preference to the land-based system 74 the onboard system mayhave means for detecting usable signals from a land-based transmitter 74and switching off the onboard transmitters 511 when such signals aredetected. This will allow users to connect to the onshore system 74.Transmitters serving areas below decks, where the onshore transmitter 74cannot be detected, may remain switched on outside territorial waters.

Instead of power control, the system may be arranged to limit the timedelay permitted on a base station to mobile station link. The time delayis usually limited to the length of one time slot in a time divisionsystem, usually 0.2 ms, a round trip time equivalent to a distance ofabout 30 km (sometimes extended to 0.4 ms (60 km) over the sea to allowextended range, by allocating two timeslots per user). By limiting thepermitted time delay to a few microseconds the effective range of thebase station can be limited to the immediate vicinity of the ship,preventing mobile units on nearby vessels using the onboard systeminstead of the terrestrial one. In this way the system can be confinedto users onboard the ship 501.

The shipboard system 501 is arranged to shut down, for example bydiscontinuing the satellite link 4-6-513, by switching off the onboarddistribution network 511, or by other means, when operating in regionswhere operation of the system is not permitted, for example withinterritorial waters. Users of mobile telephones 10 on board the ship maythen connect to the shore-based BTS 74. If the local network is not thenetwork 504 to which the onboard BTS 512 is connected, users will “roam”from the host network 504 to the local network in conventional mannerwhen such transfer takes place. However, until the user does make such atransfer, the user's home network 7 will continue to operate as if theuser is connected to the host network.

FIG. 19 shows a process according to the present invention forintercepting calls when the onboard system 2, 101, 501 is switched offat times when its operation could interfere with conventional land-basedcellular systems or with electronic control systems of the vehicle, toenforce “quiet” periods on board, or to allow transfer of the satellitelink from one satellite to another. The control to switch the system offmay be performed manually or under the control of a sensor detectinginterference from nearby radio base stations 74, or an operationalcondition of the vehicle, such as deployment of the aircraftundercarriage, low altitude, or “weight on wheels”, communicated to theonboard system by means of the control data bus 22. When such adisconnection occurs (step 1501), a signal is generated in the onboardsystem 2, 101, 501 (step 1502) for transmission over the satellite link6 to the ground station 4 (step 1503). This signal causes the satelliteground station to invoke a call failure mode for any call directed tothe onboard system 2, 101, 501 of the specified vehicle (step 1504).

Any call now diverted by the MSC 70, 141, 541 to a number correspondingto a node on board the vehicle (step 1505) will then receive a “callfailed” indication from the ground station (step 1506), without anysignalling required over the satellite link 6. Such failed calls will bere-routed according to the user's own diversion instructions, stored bythe host MSC 70, 141, 541 for use when the user's handset is busy (step1507). Generally, such instructions will be to divert the call to avoicemail system in the user's home network. In addition, the host MSC70, 141, 541 will record the existence, and possibly the origin (Callingline identity—CLI) of any such call attempts (step 1508).

When the onboard system 2, 101, 501 is re-activated (step 1511) afurther signal is transmitted by the onboard system (step 1512) fortransmission over the satellite link 6 to the ground station 4, (step1513). This signal causes the satellite ground station to revoke thecall failure mode for calls directed to the onboard system 2, 101, 501of the specified vehicle (step 1514). When a user 25, 110, 510reconnects to the onboard system 2, 101, 501 (step 1515) the onboardsystem transmits a signal to the host MSC 70, 141, 541 (step 1516) whichcauses the host MSC to retrieve the call attempt record previouslystored for that user (step 1518). If one or more such call attempts havebeen made, the MSC returns a message to the user 25, 110, 510 (step1519), prompting the user to retrieve his messages from the voicemailsystem should he so wish.

1. A method for facilitating telephone traffic between a fixed cellularnetwork and a movable network aboard a vehicle, comprising: configuringa ground-based host node to forward incoming calls from the fixedcellular network to a plurality of users through the moveable network,and to forward outgoing calls from the plurality of users;simultaneously suspending, in response to a control signal, forwardingincoming calls to the plurality of users; wherein said suspendingforwarding incoming calls does not disconnect a call in progress betweenany of the plurality of users and the fixed network; wherein saidconfiguring comprises registering routing information for atelecommunications device associated with each of the plurality of usersaboard the vehicle; and wherein said registering comprises: modifying anindividual user cellular divert on busy instructions to the deviceaboard the vehicle; and setting a status of the individual user'scellular telephone to busy regardless of the actual operating state ofthe user's cellular telephone.
 2. The method of claim 1, wherein saidsuspending incoming calls comprises de-registering the routinginformation.
 3. A ground-based host node configured to facilitatetelephone traffic between a fixed cellular network and a movable networkaboard a vehicle, comprising: a ground station configured to, inresponse to a user registration aboard a vehicle, forward incoming callsfrom the fixed cellular network to a user through the moveable network,and to forward outgoing calls from the user to the fixed network, saiduser being part of a plurality of users; the ground station beingconfigured to at least temporarily simultaneously discontinue, inresponse to a control signal, forwarding incoming calls to the pluralityof users; wherein the discontinuation in response to said control signaldoes not affect any call in progress between any of the plurality ofusers and the fixed network; wherein said ground station responds tosaid user registration by modifying the user cellular divert on busyinstructions to identify a registered location of the user aboard avehicle and setting a status of the user's cellular telephone to busyregardless of the actual operating state of the user's cellulartelephone.
 4. The ground-based host node of claim 3, wherein said groundstation discontinues forwarding incoming calls by de-registering routinginformation for a telecommunications device associated with the useraboard the vehicle.
 5. A method for facilitating telephone trafficbetween a ground-based cellular network and a movable network aboard avehicle, comprising: sending registration information of a user aboardthe vehicle to the ground-based cellular network, such that the user canreceive incoming calls and place outgoing calls from the vehicleconsistent with the user's preexisting cellular telephone account;sending a control signal representing a request for the ground-basednetwork to discontinue forwarding incoming calls to the vehicle; whereinsaid control signal does not affect a call in progress between the userand the fixed network.
 6. A method for facilitating telephone trafficbetween a fixed cellular network and a movable network aboard a vehicle,comprising: configuring a ground-based host node to forward incomingcalls from the fixed cellular network to a user through the moveablenetwork, and to forward outgoing calls from the user, said configuringcomprising modifying user cellular divert on busy instructions to thedevice aboard the vehicle and setting a status of the user's cellulartelephone to busy regardless of the actual operating state of the user'scellular telephone; suspending, in response to a control signal,forwarding incoming calls to the user; wherein said suspendingforwarding incoming calls does not disconnect a call in progress betweenthe user and the fixed network.
 7. A ground-based host node configuredto facilitate telephone traffic between a fixed cellular network and amovable network aboard a vehicle, comprising: a ground stationconfigured to, in response to a user registration aboard a vehicle,forward incoming calls from the fixed cellular network to a user throughthe moveable network, and to forward outgoing calls from the user to thefixed network; and the ground station being configured to at leasttemporarily discontinue, in response to a control signal, forwardingincoming calls to the user; wherein the discontinuation in response tosaid control signal does not affect a call in progress between the userand the fixed network; and wherein said ground station responds to saiduser registration by modifying the user cellular divert on busyinstructions to identify a registered location of the user aboard avehicle and setting a status of the user's cellular telephone to busyregardless of the actual operating state of the user's cellulartelephone.